Infusion of fluids, such as drugs and plasma, into a patient is commonplace in the medical field. Two common infusion methods are intravenous delivery of fluids by gravity and either intravenous or interarterial delivery by mechanically pressurizing the fluids for delivery to the patient. Infusion pumps with disposable cassettes have been employed with the significant advantage of providing a simple disposable element in combination with a relatively straightforward pumping action.
One infusion pump, which incorporates a cassette formed by bonding of two substantially flat sheets, has been disclosed in U.S. Pat. No. 4,657,490. With the use of such disposable cassettes the fluid to be infused into the patient comes into contact only with the cassette. The pumping mechanism itself does not contact the fluid. Thus, the cassettes and associated input and output tubing can be maintained in a sterile condition. The cassette and the tubing are disposed of and replaced between patients or between changes in the fluid to be infused. The new cassettes are loaded into an infusion pump having a cassette receiving section in which the cassette is operated upon by valve members and pumping members of the infusion pump. A pressure sensor monitors the pressure exerted on the cassette and an outlet restriction valve is controlled to maintain accuracy of delivery. The pumping stroke is timed to obtain the desired flow rate. Pressure limits can be set beyond which pumping action will not be performed.
Prior to the present invention, disposable cassette pumping systems have relied upon relatively inconvenient tubing clamps to prevent unwanted flow through the cassette to the patient before the cassette was loaded, while the cassette was being loaded and after it was removed from the cassette receiving section of the pumping mechanism. Care and attention to the external tubing clamps had to be exercised to insure that the flow was completely terminated to avoid rapid or unmetered flow to the patient. When the cassette was loaded, the external clamps were released and the valves for restricting the flow through the cassette were primarily relied upon to accomplish a selected no-flow period of operation while the cassette remained in the pumping device.
Various slide clamps which constrict or obstruct "V" lines are known, including a safety slide clamp as disclosed in Kozlo, U.S. Pat. No. 4,586,691, which comprises a blade formed with a teardrop shaped aperture through which the tubing is positioned having an enlarged portion and a narrow portion. The enlarged portion allows flow through the tubing and tapers to the narrow portion which is engageable with the tubing to prevent flow therethrough. There is a retainer for supporting the blade and retaining the tubing so that the blade can be moved with respect to the tubing to and from the open and closed positions. The clamping blade can be removed from the retainer base only upon first placing the tube into the clamped position and may be received in the base only when the blade is in the clamped position.
Another tube clamp is disclosed in U.S. Pat. No. 4,689,043 for use in a peristaltic infusion pump. It includes a slide clamp which constricts or obstructs the I.V. line similar to that as in Kozlo, however, the clamp is in that the clamp cannot be mounted into the infusion medical device unless the clamp is in the closed position. The device disclosed further cooperates with a handle which urges the clamp from a closed position to an open position when the tube is engaged in the peristaltic pumping mechanism. The handle also automatically operates to urge the clamp from the open position to the closed position prior to and in preparation of the removal of the tube from the peristaltic pumping mechanism.
Other devices are formed, such as stop cock valves, directly in the fluid path within a cast structure interposed in the fluid path. The blade clamps are improvements over such in fluid path valve structures, however currently, such flow clip blade structures either operate automatically so that the flow is automatically opened upon installation of the I.V. tube into the pumping mechanism, or must be in a closed position before installation of the clamp and flow tube into engagement with an infusion pump.
Thus, none of the foregoing art possesses in combination the advantages of the present invention in providing a reliable mechanism with the capability of completely and conveniently stopping the flow of fluid through a disposable cassette, either in or out of the pumping mechanism, such that the cassette cannot be installed unless the flow limiter is in place, such that the flow is automatically closed if the cassette is not held in an operable pumping position, such that the closing or opening of flow through the flow limiter is selectably controlled by the instrument programming when installed, such that the cassette cannot be removed until the flow is closed, such that a clip on the removed cassette can be manually moved from closed to open flow and such that a cassette is installable into the pump whether it is manually clipped closed or opened.